The PCS-DIODE is used to jump the flasher system over to a light that is to be used as a solid or flashing light. The diode only lets the power go one direction.
Your rock lights on on switch 5 and your whip lights on on switch 6, you want either to be solid or flash. Using the Diodes hook the blue wire to the right flasher circuit then the red wire to the rock light circuit. Then using a second diode hook the blue end to the left flasher circuit then the red wire to the whip light circuit. When the flasher is turned on the whips and the rock lights will flash, if you want them to be solid on then turn on the appropriate light switch, the diodes stops the power from going to the other device. If the diodes were not installed, when you turned on the rock light it would also turn on the whip lights and vise verse.